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New Member

3845 with ATM OC-3 problem


I have a router 3725 with ATM OC-3 module. ATM interface has many PVCs. All PVCs (except the one) are switched by network operator to others sites and are terminated on the Cisco routers. Some of these PVCs are translated by network operator to Frame Relay. One PVC is used to connect to the internet and is terminated by network operator. Network operator uses Nortel for ATM switching and Juniper as internet routers.

I tried to replace 3725 router with 3845 and NM-1A-OC3-POM module. All PVCs work fine except PVC to the internet. When I send a normal 64-bytes ping from 3845 router to the network operator’s router I receive the replies with a variable delay. The ping packets above 368-bytes don’t back.

I tried to use 12.4 mainline and T IOS software.

The ATM port and ATM PVC configuration is simple:

interface ATM1/0

no ip address

atm sonet stm-1

no atm ilmi-keepalive


interface ATM1/0.150 point-to-point

ip address xx.51.0.22

pvc 1/150

vbr-nrt 10000 10000

encapsulation aal5snap



Below are show commands:

rt1#show atm pvc 1/150

Description: N/A

ATM1/0.150: VCD: 3, VPI: 1, VCI: 150

VBR-NRT, PeakRate: 10000 (23585 cps), Average Rate: 10000 (23585 cps) Burst

Cells: 0 AAL5-LLC/SNAP, etype:0x0, Flags: 0x20, VCmode: 0x0, Encapsize: 12

OAM frequency: 0 second(s), OAM retry frequency: 1 second(s) OAM up retry

count: 3, OAM down retry count: 5 OAM Loopback status: OAM Disabled OAM VC

Status: Not Managed ILMI VC status: Not Managed InARP frequency: 15

minutes(s) Transmit priority 3

InPkts: 9605, OutPkts: 7832, InBytes: 2891521, OutBytes: 2643120

InPRoc: 8226, OutPRoc: 7832

InFast: 1379, OutFast: 0, InAS: 0, OutAS: 0

InPktDrops: 0, OutPktDrops: 0/0/0 (holdq/outputq/total)

CrcErrors: 0, SarTimeOuts: 0, OverSizedSDUs: 0, LengthViolation: 0,

CPIErrors: 0 Out CLP=1 Pkts: 0 OAM cells received: 0

F5 InEndloop: 0, F5 InSegloop: 0, F5 InAIS: 0, F5 InRDI: 0

F4 InEndloop: 0, F4 InSegloop: 0, F4 InAIS: 0, F4 InRDI: 0 OAM cells sent: 0

F5 OutEndloop: 0, F5 OutSegloop: 0, F5 OutRDI: 0

F4 OutEndloop: 0, F4 OutSegloop: 0, F4 OutRDI: 0 OAM cell drops: 0

Status: UP


rt1#show int atm 1/0

ATM1/0 is up, line protocol is up

Hardware is CX27470 ATMOC3

MTU 4470 bytes, sub MTU 4470, BW 149760 Kbit, DLY 80 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ATM, loopback not set

Encapsulation(s): AAL5

1023 maximum active VCs, 2 current VCCs

VC Auto Creation Disabled.

VC idle disconnect time: 300 seconds

Last input 00:00:00, output 00:00:00, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: Per VC Queueing

5 minute input rate 259000 bits/sec, 79 packets/sec

5 minute output rate 256000 bits/sec, 64 packets/sec

131383 packets input, 37252655 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

101080 packets output, 35367634 bytes, 0 underruns

0 output errors, 0 collisions, 4 interface resets

0 output buffer failures, 0 output buffers swapped out rt1#



Re: 3845 with ATM OC-3 problem


I've seen problems on some platforms/cards where a missing MBS parameter causes problems. Could you try the following config:

interface ATM1/0.150 point-to-point

ip address xx.51.0.22

pvc 1/150

vbr-nrt 10000 10000 1

encapsulation aal5snap


Hope that helps - pls rate the post if it does.


New Member

Re: 3845 with ATM OC-3 problem

I was having a similar problem.

My carrier Telstra Australia came up with the following:

Have you got a Cisco login if so have a look at this bug which effects

your IOS while not exactly the same scenario it is suspicious


Symptoms: Packets may exceed the PCR, causing large packets to be

dropped by

an ATM switch.

Conditions: This symptom is observed when a VBR-nrt PVC is configured on


NM-1A-OC3-POM network module with the PCR identical to the SCR and when


cell delay variation tolerance (CDVT) is violated at low traffic rates.


symptom may also occur when a CBR PVC is configured on an NM-1A-OC3-POM

network module.

Workaround: Set the SCR to a slightly lower value than the PCR or do not

configure a CBR PVC. Verify that the SCR and PCR settings are correct by

entering the show controller atm

slot/port command and ensuring that the SCR is a value

other than 0, as in the following command output example:

Tx bytes (489890600), Tx packets (360325), PCR/SCR (10240/10230)




You may want to try as Cisco suggest to set the SCR below the PCR and

see how close you can approach to the 4096 value.



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